South Korea's financial regulator said Monday it has begun monitoring markets around the clock and will swiftly act if necessary, after North Korea spiked tensions by conducting its sixth and most powerful nuclear test.

Zhin Woong-seob, governor of the Financial Supervisory Service, held a meeting earlier in the day to review contingency measures.

"It is difficult to predict the situation on the Korean Peninsula as North Korea went ahead with a nuclear test, despite intense sanctions by the international community," Zhin told the meeting, according to a statement released by the FSS.

US Defense Secretary Jim Mattis said Washington will make a "massive military response" to any threats from North Korea, while North Korea said the sixth nuclear test was based on an advanced hydrogen bomb that can be mounted on a long-range ballistic missile.

Zhin said tensions on the Korean Peninsula could rise to its "highest level" over a confrontation between North Korea and the United Sates.

The FSS said it will hold a meeting with bank executives later in the day to monitor currency movements.

South Korea's financial market is vulnerable to heightened geopolitical risks from North Korea, with the latest provocation highlighting this point. (Yonhap)